1. Field of the Invention
The present invention relates to packagers and in particular to a method for the stacking in layers of timber packages, an arrangement for the stacking in layers of timber packages, and the use of carrier planes in a packagers.
2. Description of the Related Art
Several different methods and arrangements for the stacking in layers of sawn timber are known. These include such methods and arrangements in which the timber is collected in layers on an input transporter and fed forwards in its transverse direction, and from which transporter layers of a pre-determined width are separated and transferred by means of transfer arms that are mobile in a forwards and backwards direction and that are designed as carrier planes to a packaging lift, whereby a package of layers laying one on top of another is formed. The lift is arranged to descend according to a program at the rate at which the package layers are collected on the carrier arms of the lift such that space is made available for the transfer of the subsequent layer. Stacking laths can be used between the layers during the packaging operation in order to promote drying of the package, depending on whether the timber that is to be packaged is dry or fresh. The said transfer arms that perform forwards and backwards motion are designed as a number of parallel fingers that are transverse to the longitudinal direction of the pieces of timber and are evenly distributed, arranged to lift from below layers of pieces of timber from the input transporter and subsequently to transport the layer in an essentially horizontal direction in over the lift arrangement. The transfer arms are subsequently drawn back while the layer of timber is scraped off from the transfer arms whereby the layer is placed directly onto the carrier arms of the lift arrangement if it is a case of the lowermost layer in a package, or onto the uppermost layer of timber in the lift arrangement, if layers of timber have been previously laid.
In order to scrape the layer from the transfer arms, retaining means that act against one edge of the layer function as counterpieces and in this way retain the layer over the lift arrangement while the transfer arms are withdrawn in the direction of the input transporter. There is, however, the problem, particularly with slender timber, that the pieces of timber tend to tip or become disorganised when the transfer arms are withdrawn. In order to solve the said problem, the solution of providing a holder is known, which holder can be brought from a withdrawn resting position to interact with the upper surface of the layer of timber and in this way to press down in a retaining manner the most recently laid layer of timber while the transfer arms are withdrawn from the layer. It should be understood in this part that the holder must be withdrawn such that it is located in a position that does not interfere when a new layer of timber can be placed onto the uppermost layer of timber in the lift arrangement. Consequently, the said holder as such is considerably limiting for the speed with which a packager can be run.
In addition to the holder that acts on the upper surface of the layer, the large forces that act on the transfer arms when these are displaced forwards and backwards while at the same time being lifted lead to limitations on achieving the desired transfer speeds. Furthermore, it becomes a requirement that it should be possible to handle with accurate control the layers of timber that are lying on the transfer arms, despite the large forces of acceleration and retardation that may arise during the transfer, and also that it is possible to achieve this when handling timber that differs considerably in dimension.
In the prior art forms of packager and packaging machines there is a striving to be able to increase the speed of the machine, and thus their capacities, from the current value of approximately 20 layers of timber per minute to 30 layers of timber per minute, or greater, i.e. to a capacity that corresponds to at least one layer of timber every 2 seconds.
U.S. Pat. No. 4,290,723 reveals a packager that is provided with a first and a second carrier plane that are cyclically mobile on arms. The carrier planes are arranged to lift one layer of timber at a time from the end of an input transporter down onto a stacking table, after which the layer is scraped from the carrier plane in interaction with a counterpiece that is arranged at the stacking table. The stacking cycle is so arranged that the two carrier planes, which follow one after the other, are located at a position under the input transporter, where the second carrier plane is located in a position of preparedness behind the first carrier plane, with the same gradient as this first plane, while the first carrier plane is filled with a layer of timber.